1. Field of the Invention
The present invention relates generally to a method of manufacturing contact holes in an integrated circuit, and more particularly to a method of manufacturing contact holes indifferent regions, such as in a logic region and in a static random access memory (SRAM) region simultaneously.
2. Description of the Prior Art
Field effect transistors are important electronic devices in the fabrication of integrated circuits. As the sizes of the semiconductor devices becomes smaller and smaller, the fabrication of the transistors also has to be improved so as to fabricate transistors with smaller sizes and higher quality.
For a static random access memory (SRAM) comprised of transistors, the transistors are often electrically connected with one another through contacts and metal lines. By electrically connecting a portion of one transistor to a portion of another transistor, every six of the transistors can constitute a latch circuitry as well as a unit cell of the SRAM. Also, as the size of the SRAM continues to shrink, there is also a need to dispose contacts between the transistors and the metal lines of the SRAM, and these contacts are sometimes called M0 contacts. Generally, M0 contacts are formed on or above source/drain regions of the transistors and are often used to provide a short-distance electrical connection. However, because the densities of the M0 contacts are varied from region to region, the resolution of the corresponding photolithographic process for manufacturing the M0 contacts is often lowered by this non-uniform contact density.
Accordingly, there is still a need to provide a modified method for manufacturing contact structures, especially M0 contacts, in order to overcome the above-mentioned drawbacks.